1. Field of the Invention
The present invention relates to a method of manufacturing a micro floating structure capable of providing improved device yield.
2. Description of the Related Art
A micro floating structure as mentioned above is used as an inertia weight, a spring or the like in a sensor such as an accelerometer or gyroscope. A conventional method of manufacturing such a micro floating structure is illustrated in FIGS. 1A to 1E.
Referring to FIGS. 1A and 1B, according to the conventional method, first and second oxide films 12, 22 are formed on one surface of each of first and second substrates 10, 20, respectively, and then the first and second substrates 10, 20 are bonded to one another such that the first and second oxide films 12, 22 face one another.
Then, the second substrate 20 is polished to a thickness of the floating structure 30 (see FIG. 1D), as shown in FIG. 1C.
Next, the polished second substrate 20 is subjected to photolithographic and dry etching processes to form the floating structure 30, as shown in FIG. 1D.
Then, if the first and second oxide films 12, 22 formed underneath of the floating structure 30 are removed by wet etching, the floating structure 30 is in a state in which the bottom surface thereof floats above the first substrate 10, as shown in FIG. 1E.
During the manufacturing process described above, dry etching is performed by bombarding ion beams against the polished second substrate 20. However, if the second oxide 22 is exposed while the etching is proceeding, ion beams are injected into the second oxide film 22 whereby the second oxide film 22 becomes charged. If so, the path of subsequent ion beams will be changed by the electrostatic force of the second oxide film 22, and the path-changed ion beams will produce notches 32 on the bottom side of the floating structure 30. Although the drawing shows several notches 32 on floating structure 30 formed thereby, a countlessly large number of fine notches 32 are practically formed on the bottom side of each floating structure 30. Such notches 32 change the physical properties such as mass and spring constant of the floating structure 30, thereby causing an error from a design value. In addition, the path-changed ion beams will produce needle-shaped by-products ablated from the notches 32 while the notches 32 are being formed. Such needle-shaped by-products can interconnect certain spaced parts in the floating structure 30, thereby causing an electric short in the floating structure 30.
On the other hand, the first and second oxide films 12, 22 formed below the floating structure 30 are removed by wet etching, wherein the etchant contained in the wet etching liquid causes a capillary phenomenon (or so-called stiction phenomenon), which causes adhesion between the various parts in the floating structure 30 or between the first substrate 10 and the floating structure 30.
Notches generated in the floating structure 30, and electric shorts caused by a needle-shaped by-product and the stiction phenomenon are main detractors of device yield in producing a floating structure 30.